The present invention relates generally to the field of printing. In particular, an apparatus for expelling a warmed fluid curtain over a freshly printed surface of a media adjacent a printing zone through apertures designed to create a fluid flow at the printed surface adequate for promoting drying of the entire freshly-printed surface. In combination with said fluid flow a separate fluid recovery pathway evacuates ink vapors, dust, and particulates created during printing so they can be appropriately contained or vented.
The present invention addresses a need in the art to reliably and safely increase throughput of large format ink jet print engines. One constraint impeding the ability to increase printing speed (typically expressed as a square foot/hour measurement) of large format ink jet print engines is ink drying characteristics and the amount of ink expelled upon the media (or xe2x80x9cink coveragexe2x80x9d typically expressed as a percentage of coverage by a given color of ink). The physical make up of the printing surface, any coatings present on the printing substrate, the type of ink applied, and whether any post-printing drying or vapor recovery treatment(s) are applied all contribute to a reliable and safe rate of throughput for large format print engines.
Ambient conditions affect the ability to print high quality prints at an efficient rate of throughput. In fact, a rise of relative humidity (RH) of just a few percent can inhibit ink drying in at least two ways. First, if the printing media is not insulated from the rising humidity, the media itself can acquire a moisture content that will in effect displace the ink that is later applied, with the result that the media simply cannot absorb as much ink as when it is xe2x80x9cdry.xe2x80x9d Second, if the ambient atmospheric conditions become saturated, the ability of the ink to dry (or be absorbed into the ambient air) is inhibited and thus, printed output will dry only slowly. Particularly with roll-based media printed in quantity (or banner prints), if printed media is not fully dry after printing the print might transfer to the back of an adjacent portion of media, or smudge, when the printing substrate is rolled prior to cutting into individual images.
In the prior art, a variety of forced air dryers have been employed to increase the evaporation and drying of ink printed onto a section of media. In addition, some prior art approaches link one or more atmospheric sensors to a printing control unit to slow printing operations when ambient conditions do not promote drying. Also, some prior art techniques have used a xe2x80x9cmedia loopxe2x80x9d (in conjunction with a proximity sensor disposed to sense the presence of said media loop) wherein the just-printed media passively hangs prior to being rolled to thereby increase the drying time, or exposure of the media to ambient drying conditions.
When the type of inks used contain agents to promote drying, or when the ink itself releases vapors and possibly harmful air-borne material, a dedicated system for removing said vapors or possibly harmful air-borne material has been implemented in large-scale printing systemsxe2x80x94but to the inventors"" knowledge no such system has even been combined into a single unit, nor adapted to operate in conjunction with a single large format thermal ink jet print engine.
The present invention thus finds utility over a variety of printing platforms that operate to simply expel air in the vicinity of printed output and also offers vapor recovery/evacuation from a common assembly so that thermal ink jet printing can be successfully practiced over a large variety of atmospheric conditions and in conjunction with a large variety of solvent-based inks compositions.
The apparatus of the present invention increases the operating envelope for large format thermal ink jet printing via a directed fluid flow from specially-designed orifices which promote an approximately equal fluid flow over an entire printed surface adjacent a printing zone in a large format ink jet printer where in addition to the optimized fluid flow one or more heating elements are inserted directly into the fluid flow to thereby promote drying of said printed surface. In the exemplary embodiment, dual fans each supply a plenum chamber with a constant supply of forced air that immediately interacts with heated metal coils of an in-line heater unit which raises the temperature of the air approximately 20 degrees Fahrenheit. As a result of this increase in air temperature the air is able to carry far more moisture than if the air were at ambient conditions. As an example, if the air were to rise 10 degrees Celsius traditional calculations indicate that about double the amount of moisture can be absorbed into the air. In the embodiment just described, each fan is rated at 30 cubic feet per minute.
In one embodiment, a single dual-duct plennum spans the width of a roll-fed large s format ink jet print engine and a first duct distributes heated air downward (in the direction of media web movement) and a second duct evacuates a printing space so that any potentially harmful ink vapors or other air-borne contaminant is appropriately fluidly coupled to either a remote exhaust vent or vapor capture vessel.
The following figures are not drawn to scale and only detail a few representative embodiments of the present invention, more embodiments and equivalents of the representative embodiments depicted herein are easily ascertainable by persons of skill in the digital imaging arts.